Agradecimentos: The authors thankfully acknowledge Marie-Josée Lévesque, Christine Maynard and Sylvie Sanschagrin for their assistance with the biomolecular techniques (DNA extraction, purification and PCR) and sequencing (through Ion TorrentTM); and also, Stephane Deschamps and Alain Corriveau for their valuable contribution with physicochemical analysis (HPLC and gas chromatography of alcohols). This work was supported by FAPESP – Fundação de Amparo a Pesquisa do Estado de São Paulo (processes 2010/18.463–9 and 2013/18.172–2 – G. Mockaitis and 2009/15.984–0 – M. Zaiat), and the NRC – National Research Council of Canada (project A1-004645 – S.R. Guiot) Ver menos

Abstract: This work reports the effect of four different physicochemical pretreatments (acidic, thermal, acidic-thermal, and thermal-acidic) on an anaerobic inoculum aiming at alcohols production, using acetate and butyrate as carbon sources and hydrogen as co-substrate. Pretreatments were carried out to select microbial communities more able to use hydrogen to metabolize volatile fatty acids into their respective alcohols. Experiments were conducted in single batches using acetate and butyrate as substrates at 30 °C and with a pressurized headspace of pure H2 at 2.15 atm (218.2 MPa). Thermal and acidic-thermal pretreatments lead to higher production of both ethanol and butanol, indicating that these pretreatments successfully selected communities more suitable for acetate and butyrate solventogenesis. Kinetics modelling shows that the highest attainable concentrations of ethanol and butanol produced were 122 mg L-1 and 97 mg L-1 for the thermal pretreatment (after 17.5 days) and 87 mg L-1 and 143 mg L-1 for the acidic-thermal pretreatment (after 18.9 days). Process thermodynamics indicated that high H2 partial pressure favoured solventogenic metabolic pathways. Sequencing data showed that both thermal and acidic-thermal pretreatments selected mainly the bacterial genera Pseudomonas, Brevundimonas, and Clostridium. Acidic-thermal pretreatment selected a bacterial community more adapted to the conversion of acetate and butyrate into ethanol and butanol, respectively. Thermal-acidic pretreatment was unstable, showing significant variability between replicates. Acidic pretreatment showed the lowest alcohol production Ver menos